System for Controlling Voltage Balancing in a Plurality of Lithium-Ion Cell Battery Packs and Method Thereof

ABSTRACT

Disclosed are system and method for adjusting a voltage balancing of cell in a lithium ion multicell battery pack The system comprises a multicell battery pack including a master module and a slave module; a CPU located in the system controller and outputting a synchronization signal for each of cells in the master module and the slave module, a first vertical interface transmitting the synchronization signal outputted from the CPU to the master module; and a second vertical interface transmitting the synchronization signal to the slave module through the first vertical interface. Accordingly, it is possible to read voltages of all cells in the one battery pack with a same timing and thus to prevent a cell voltage reading error due to the voltage reading time difference, thereby increasing an accuracy of a voltage balancing of the cells.

TECHNICAL FIELD

The invention relates to a battery balancing system reading voltages ofcells in a multicell battery pack and comparing the read voltages tocharge or discharge the cells, and more particularly to a batterybalancing system and method for reading voltages of all cells in abattery pack with a same timing so as to eliminate a cell voltagereading error due to a voltage reading time difference.

BACKGROUND ART

In general, a battery power supply unit is an electric power sourcesupplying an energy to a related electronic device and a multicellbattery pack is applied as the supply unit. By using the multicell pack,rather than a single cell, it is possible to apply a high voltage or toincrease a capacity. However, since the cell itself has charge/discharge characteristics, a voltage of each cell tends to be unbalancedas time goes by.

The voltage difference between the cells in the battery pack maygenerate an un- balancing between the battery cells, thereby causing acapacity loss of the battery pack. With regard to this, it has beendeveloped various battery balancing systems and methods for balancingeach cell so as to prevent overcharges of all battery cells and touniformly charge the cells.

For example, there is a method of allowing a current to flow to a highvoltage cell of cells in a battery pack through a resistance and thelike so as to adjust a cell balancing. Although this method is simple,it has a disadvantage that a discharge current is increased and heat ismuch generated if the number of unbalanced high voltage cells isincreased. In addition, the method has also a disadvantage that thebalance is adjusted to a cell having the lowest voltage of the cells inthe battery pack.

In addition, there is a method of allowing a charge current to flow to alow voltage cell of cells in a battery pack so as to adjust a balancing.This method uses a DC-DC converter and has advantages that efficiency isgenerally high and heat is less generated.

However, the method has also a disadvantage that a cell voltage of theentire battery pack becomes lower than its original lowest voltage ifthe number of low voltage cells is increased.

Further, there is a considerable difference between read voltages due toa reading timing difference when a voltage of each cell is read. Due tothe voltage reading timing difference, the battery balancing systemdecides that the cells are unbalanced.

It will be described a difference of voltage values according to thevoltage reading time of each cell, with reference to FIGS. 1 and 2.

FIG. 1 is a schematic view showing an apparatus for adjusting a voltagebalancing using a line selecting device in a lithium ion cell batteryaccording to the prior art and

FIG. 2 is a view illustrating a voltage reading timing in a lithium ioncell battery according to the prior art.

Referring to FIG. 1, in the prior voltage balancing adjusting apparatus,when load current flows through a load device 5, terminal voltage ofcells are sensitively changed as the load current is varied. The load ofthe load device 5 is varied as time goes by. Accordingly, when thevoltages of the cell terminals are read and compared in a CPU 3 througha line selecting device 1, the voltage value of each cell terminal isdifferently read even though the voltages of all cells are substantiallybalanced. As a result, the CPU 3 decides that each of the cells isunbalanced, and thus outputs a balance control signal to control abalance current control section 4.

Referring to FIG. 2, when the cell terminal voltages are read throughthe line voltage selecting device 1 in the battery balancing system, itcan be seen that the cell terminal voltages are not varied if the loadcurrent is not changed in the cells (B1, B2, B3, B4). Accordingly, theCPU 3 decides that the voltage of the cell terminal is balanced.However, the terminal voltages of the cells are varied when the loadcurrent is changed. Accordingly, when the load current is changed inreal-time, the CPU 3 decides that the voltages of the cell terminals areout of balance, due to the voltage reading difference resulting from theload variance as time goes by.

Like this, when the CPU 3 reads the terminal voltages of the cells usingthe line selecting device 1, the read voltage values of the cells may bedifferent due to the difference of times at which the terminals areselected.

Therefore, it is required a battery balancing system or method capableof eliminating a voltage reading error of cells in a cell system,rapidly performing a voltage balancing and increasing an accuracy of avoltage balancing.

The battery balancing system according to the prior art has diversecondition limitations. For example, it performs a voltage balancing onlywhen the system itself is not operated. Due to the limitations, thevoltage balancing operation becomes complicated, an unnecessary time isconsumed and an accuracy of the voltage balancing is decreased.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the invention has been made to solve the problems occurringin the prior art. An object of the invention is to read a cell terminalvoltage in a lithium ion cell battery after holding the voltage for asame retention time and thus to eliminate a reading error of the cellvoltage resulting from a change of the terminal voltage as time goes by,thereby improving an accuracy of a cell balancing.

Another object of the invention is to receive voltage data of anotherbattery pack via communication means in a battery balancing systemconsisting of a plurality of battery packs so as to adjust a voltagebalance of a battery pack or to receive a target value of a voltagebalance so as to adjust a voltage balance.

Technical Solution

In order to achieve the above objects, there is provided a cellbalancing adjusting system adjusting a voltage balancing of cells in alithium ion multicell battery pack and having a system controller, thesystem comprising: a multicell battery pack consisting of a mastermodule and a slave module, a CPU located in the system controller andoutputting a synchronization signal for each of cells in the mastermodule and the slave module, a first vertical interface transmitting thesynchronization signal outputted from the CPU to the master module and asecond vertical interface transmitting the synchronization signal to theslave module via the first vertical interface.

According to an embodiment of the invention, the synchronization signalmay comprise a signal for synchronizing the cells of the master moduleand a signal for synchronizing the master module and the slave module.

In addition, the synchronization signal may comprise a signal forsynchronizing an interval of a plurality of multicell battery packs.

According to a preferred embodiment of the invention, the CPU may outputa reading hold signal for holding instantaneous voltages of the cells inthe multicell battery pack and a reading balance signal for performingreading and balancing of all cell voltages.

According to a preferred embodiment of the invention, the verticalinterface may comprise a photo coupler transmitting the synchronizationsignal in parallel.

According to another aspect of the invention, there is provided abattery balancing system comprising a plurality of multicell batterypacks including a first CPU reading terminal voltages of cells in amaster module and a slave module, a system controller collecting,calculating and controlling cell related data from the multicell batterypacks, a second CPU installed in the system controller and receivingdata of all cells in the multicell battery packs to provide a balancingtarget value necessary for each of the battery packs, and a DC-DCconverter controlling a direction of current flowing to each cell, basedon the target value, to adjust a voltage balance.

According to a preferred embodiment of the invention, the second CPU maycompare the balancing target value and the voltage of each cell andcontrol a current direction of the DC-DC converter so that a balancingcurrent flows to a charge direction in a cell when the voltage of thecell is lower than the balancing target value.

According to a preferred embodiment of the invention, the second CPU maycompare the balancing target value and the voltage of each cell andcontrol a current direction of the DC-DC converter so that a currentflows to a discharge direction in a cell when the voltage of the cell ishigher than the balancing target value.

According to a preferred embodiment of the invention, the data maycomprise a maximum voltage, a minimum voltage and a mean value thereof.

According to a preferred embodiment of the invention, the second CPU mayoutput a synchronization signal for synchronizing the multicell batterypacks.

According to a preferred embodiment of the invention, the balancingsystem may further comprise a vertical interface provided between themulticell battery packs and transmitting the synchronization pulse.

Advantageous Effects

According to the invention, the terminal voltages of the cells are readwith a same timing in the lithium ion cell battery, thereby improving anaccuracy of the voltage balancing.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view showing an apparatus adjusting a voltagebalancing using a line selecting device in a lithium ion cell batteryaccording to the prior art;

FIG. 2 is a view showing a voltage reading timing of cells in a lithiumion cell battery according to the prior art;

FIG. 3 shows a voltage balancing system for cells in a multicell batterypack according to an embodiment of the invention; and

FIG. 4 is a view showing a voltage reading timing of cells in a lithiumion cell battery according to an embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescriptions of the present invention, a detailed description of knownfunctions and configurations incorporated herein will be omitted when itmay make the subject matter of the present invention rather unclear.

FIG. 3 is a block diagram of a system performing a voltage balancing ofcells of a plurality of multicell battery packs 2, 7, 8, 9 according toan embodiment of the invention.

The system comprises the plurality of multicell battery packs 2, 7, 8, 9and a system controller 1.

The system controller 1 comprises a CPU 1-1, and collects and calculatesdiverse cell related data of each battery pack from the plurality ofmulticell battery packs 2, 7, 8, 9 and system inside sensors 1-4, 1-5,1-13, thereby controlling the whole system. In addition, the controller1 transmits data or a control signal to an apparatus using the pluralityof multicell battery packs.

Output terminals of cells (4S+4S) of the multicell battery pack 2 areconnected in series. A highest output terminal (TB+) and a lowest outputterminal (TB−) of the multicell battery pack are used as a power outputterminal of the system.

In addition, the output terminal (TB−) of the multicell battery packpasses through a current detecting device 1-4 and an emergencyinterception device 1-8. The current detecting device 1-4 is provided todetect current flowing in a cell and a resistance or Hall device is usedas the current reading device.

The multicell battery pack 2 comprises a CPU 2-1, a DC-DC converter 2-2,an auxiliary switch 2-3, a master module 3 and a slave module 5.

The master module 3 and the slave module 5 have a substantially samestructure.

The master module 3 comprises four cells 4S, a protecting circuit 3-1and a balance control circuit 4. The slave module 5 comprises four cells4S, a protecting circuit 5-1 and a balance control circuit 6. Thebalance control circuits 4, 6 have a function of converting a terminalvoltage of each cell into a ground potential so that the CPU 2-1 canread the terminal voltage.

The balance control circuits 4, 6 of the master module 3 and the slavemodule 5 are respectively structured such that they can transmit/receivea signal through a vertical interface 6-1 (VIF). In addition, a verticalinterface 4-1 in the balance control circuit 4 of the master module 3can transmit/receive a signal with the multicell battery pack 7 belowthereof. The signal comprises a signal for synchronizing the multicellbattery pack 2 and a signal for synchronizing an interval of themulticell battery pack 2 and the multicell battery packs 7, 8, 9. Thesesignals are transmitted/received between all the multicell battery packs2, 7, 8, 9 through the vertical interfaces, thereby synchronizing allthe battery packs.

Hereinafter, a cell balancing operation will be described with referenceto the above structure.

In a battery balancing system according to an embodiment of theinvention, the CPU 2-1 of the multicell battery pack 2 reads a terminalvoltage of each cell in the master module 3 and the slave module 5. Theread voltage data is transmitted to the CPU 1 -1 of the systemcontroller 1 via a local communication interface 2-4.

The balance control circuit 4 has an alternation switch so that abalance current can flow in each cell. The alternation switch can becontrolled by the CPU 2-1.

The DC-DC converter 2-2 is inputted with outputs (TB+, TB−) of themulticell battery pack. In addition, the DC-DC converter 2-2 controlsthe auxiliary switch 2-3 and the balance control circuit 4 to enable thebalance current to flow in each of the cells.

The CPU 1-1 of the system controller 1 receives data of a maximumvoltage, a minimum voltage, a mean value thereof and the like of allcells in the battery pack and provides a balancing target valuenecessary for each battery pack.

Based on the balancing target value, each multicell battery packcontrols the current and thus adjusts a balance thereof. In addition,the CPU 1-1 compares the balancing target value and a voltage of eachcell and controls a current direction of the DC-DC converter so that abalancing current flows to a charge direction if the voltage of the cellis lower than the balancing target value. On the contrary, if thevoltage of the cell is higher than the balancing target value, the CPUcontrols a current direction of the DC-DC converter so that a currentflows to a discharge direction in the cell.

Like this, since the balancing target value is continuously renewed, abalancing of the whole system can be adjusted.

In addition, according to an embodiment of the invention, voltages ofall the cells are preferably read at the same time. Accordingly, the CPU1 -1 outputs a synchronization pulse RB (reading & balance pulse) and asynchronization pulse RH (reading hold pulse).

Hereinafter, the synchronization pulses (RB, RH) outputted by the CPU1-1 will be described with reference to FIG. 4.

FIG. 4 shows that the CPU 1-1 of the system controller 1 outputs thesynchronization pulses to read terminal voltages of the cells with asame timing, according to an embodiment of the invention.

Referring to FIG. 4, when the CPU 1-1 outputs the reading hold pulse(RH), instantaneous voltages of the cells in all the multicell batterypacks are held, so that all the cells can carry out the reading and thebalancing of the cell voltage with a same timing by the reading balancepulse (RB).

Like this, the voltage balancing system of the invention transmits thesynchronization pulses thereof to the vertical interface 6-1 of theslave module 5 via the vertical interface 4-1 of the master slave 3.

In addition, the synchronization pulses are sequentially transmitted tothe vertical interface 6-1 of the multicell battery pack 2 through thevertical interface in the master module of the multicell battery pack 9.Thereby, the system having the plurality of multicell battery packs canalso read the terminal voltages of all the cells in each of the batterypacks with a same timing.

In the above embodiment, the two synchronization pulses (RB, RH) areused to synchronize the battery balancing system. However, the batterybalancing system may be synchronized with one synchronization pulseonly. In addition, although the synchronization signals are sequentiallytransmitted using the vertical interface, they may be transmitted inparallel using a photo coupler.

Hereinafter, a multicell battery pack will be specifically describedwith reference to FIG. 5.

Referring to FIG. 5, a cell alternation switch of the balance controlcircuit 4 of the master module 3 comprises a current switch 4-5 and avoltage switch 4-4.

Since the current switch 4-5 enables the balance current to flow, aswitch device having a large current capacity is used. Since the voltageswitch 4-4 reads the terminal voltage of the cell, its current capacitymay not be large.

In addition, since the voltage switch 4-4 has a hold function, it canmeasure voltages with a same timing.

A control section 4-3 controls a cell address or performs a holdcontrol. The cell address receives an address clock (AdrClk) pulse fromthe CPU 2-1 and selects one of the cells (B1, B2, B3, B4).

The address clock (AdrClk) pulse is converted into a signal level of thebalance control circuit at a signal level of the CPU through aninterface 4-2. The balance hold pulse (BH) is also converted into asignal level of the balance control circuit at a signal level of the CPUthrough the interface 4-2. The balance hold pulse is provided to readthe cell voltage during the balance period. The reading hold pulse (RH)is inputted to synchronize all the multicell battery packs, from theexterior. However, the balance hold pulse (BH) is not synchronized withthe other multicell battery packs and is outputted from the CPU 2-1 soas to perform the voltage reading with an individual timing.

When the reading balance pulse (RB) is inputted into the multicellbattery pack, an operating state becomes under reading mode, the currentswitch is off and the cell (B1) is addressed. When the reading holdpulse (RH) is inputted into the battery pack, the cell voltage is heldin a condenser. Then, when the address clock (AdrClk) is once inputted,the cell (B2) is addressed.

In addition, the voltage switch 4-4 is not directly connected to thecells (B1˜B4) but connected to the condenser holding the voltages of thecells (B1˜B4).

The current switch 4-5 is directly connected to the cells (B1, B2, . . .). The current switch 4-5 is off at the reading balance mode. If thebalance address is shifted to pass over the cell (B4), the switch of themaster module is off and the switch of the slave module is on.

Like this, when the cells are sequentially shifted from the cell (B1) tothe cell (B4), it again comes back to the cell (B1). The voltages fromthe cell (B1) to the cell (B4) are read in such a manner. By repeatedlyreading the voltages from the cell (B1) to the cell (B4), it is possibleto increase an accuracy of the cell balancing.

Each cell voltage from the voltage switch 4-4 is fixed at the groundsince the hold voltage is being read. Accordingly, the voltage of themaster module can be directly read with the CPU, but the voltage of theslave module is connected to the ground potential through a calculationamplifier 2-10 since it is required to shift the voltage of the slavemodule into the ground voltage.

When it is converted to the balance mode from the reading balance mode,the current switch 4-5 is on. Also in the balance mode, the voltage isrepeatedly measured in sequence from the cell (B1) to the cell (B4).

When it is desired to enable the current to flow to one of the cells,the CPU 2-1 outputs an on/off control signal to make the balance currenton.

Although the on/off of the balance current is described with thefunction of the auxiliary switch 2-3, it can be also performed with theDC-DC converter 2-2 or current switches 4-5, 6-5.

The current switch cannot be directly connected since the groundpotentials of the master module and the slave module are different.Accordingly, the auxiliary switch 2-3 is used. The auxiliary switch 2-3turns on the switch of the master module in case that it addresses thecells (from B1 to B4) by the control signal of the controller 4-3, andturns on the switch of the slave module in case that it addresses thecells (from B5 to B8).

In conclusion, the reading hold pulse (RH) and the reading balance pulse(RB) are transmitted from the master module to the slave module throughthe vertical interface 4-1. Thereby, it is possible to read the voltagesof the cells (B1˜B8) with a same timing and thus to prevent the voltagereading error due to the timing difference.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A system for adjusting a battery balancing, having a systemcontroller and adjusting a voltage balancing of cells in a lithium ionmulticell battery pack, the system comprising: a multicell battery packincluding a master module and a slave module; a CPU located in thesystem controller and outputting a synchronization signal for each ofcells in the master module and the slave module, a first verticalinterface transmitting the synchronization signal outputted from the CPUto the master module; and a second vertical interface transmitting thesynchronization signal transmitted through the first vertical interfaceto the slave module.
 2. The system according to claim 1, wherein thesynchronization signal comprises a signal for synchronizing the cells ofthe master module and a signal for synchronizing the master module andthe slave module.
 3. The system according to claim 1, wherein thesynchronization signal comprises a signal for synchronizing an intervalof a plurality of multicell battery packs.
 4. The system according toclaim 1, wherein the CPU outputs a reading hold signal for holdinginstantaneous voltages of the cells in the multicell battery pack and areading balance signal for performing reading and balancing of all cellvoltages.
 5. The system according to claim 1, wherein the verticalinterface comprises a photo coupler for transmitting the synchronizationsignal in parallel.
 6. A battery balancing system comprising: aplurality of multicell battery packs comprising a first CPU for readingterminal voltages of cells in a master module and a slave module; asystem controller for collecting and calculating cell related data fromthe multicell battery packs; a second CPU installed in the systemcontroller and for receiving data of all cells in the multicell batterypacks to provide a balancing target value required for each of thebattery packs; and a DC-DC converter for controlling a direction ofcurrent flowing to each cell, based on the target value, to adjust avoltage balance.
 7. The system according to claim 6, wherein the secondCPU compares the balancing target value and a voltage of each cell andcontrols a current direction of the DC-DC converter so that a balancingcurrent flows to a charge direction in a cell when the voltage of thecell is lower than the balancing target value.
 8. The system accordingto claim 6, wherein the second CPU compares the balancing target valueand a voltage of each cell and controls a current direction of the DC-DCconverter so that a current flows to a discharge direction in a cellwhen the voltage of the cell is higher than the balancing target value.9. The system according to claim 6, wherein the data comprises a maximumvoltage, a minimum voltage and a mean value thereof.
 10. The systemaccording to claim 6, wherein the second CPU outputs a synchronizationsignal for synchronizing the multicell battery packs.
 11. The systemaccording to claim 6, further comprising a vertical interfacetransmitting the synchronization pulse between the multicell batterypacks.
 12. A method for adjusting a voltage balancing of cells in alithium ion multicell battery pack, the method comprising steps of:outputting a synchronization signal for a cell of a master module in themulticell battery pack module to the master module through a firstvertical interface; and transmitting the synchronization signaltransmitted through the first vertical interface to a slave module inthe multicell battery pack through a second vertical interface.
 13. Themethod according to claim 12, wherein the synchronization signalcomprises a signal for synchronizing cells of the master module and asignal for synchronizing the master module and the slave module.
 14. Themethod according to claim 12, wherein the synchronization signalcomprises a signal for synchronizing a plurality of multicell batterypacks.
 15. The method according to claim 12, wherein the synchronizationsignal comprises a reading hold signal for holding instantaneousvoltages of the cells in the multicell battery pack and a readingbalance signal for performing reading and balancing of all cellvoltages.
 16. The method according to claim 12, wherein the verticalinterface comprises a photo coupler transmitting the synchronizationsignal in parallel.
 17. A battery balancing method comprising the stepsof: reading terminal voltages of cells in a master slave and a slavemodule; collecting and calculating data relating to the cells, based onthe read terminal voltages; receiving data of all the cells in themulticell battery packs to provide a balancing target value required foreach of the battery packs; and controlling a direction of currentflowing to each of the cells to perform a voltage balancing, based onthe target value.
 18. The method according to claim 17, furthercomprising a step of comparing the balancing target value and a voltageof each cell, wherein the step of performing the voltage balancingcomprises a step of controlling a current direction so that a balancingcurrent flows to a charge direction in a cell when the voltage of thecell is lower than the balancing target value.
 19. The method accordingto claim 17, further comprising a step of comparing the balancing targetvalue and a voltage of each cell, wherein the step of performing thevoltage balancing comprises a step of controlling a current direction sothat a balancing current flows to a discharge direction in a cell whenthe voltage of the cell is higher than the balancing target value. 20.The method according to claim 17, wherein the data comprises a maximumvoltage, a minimum voltage and a mean value thereof.
 21. The methodaccording to claim 17, further comprising a step of outputting asynchronization signal for synchronizing the multicell battery packs.22. The method according to claim 12, further comprising a step oftransmitting the synchronization pulse between the multicell batterypacks.
 23. The system according to claim 2, wherein the CPU outputs areading hold signal for holding instantaneous voltages of the cells inthe multicell battery pack and a reading balance signal for performingreading and balancing of all cell voltages.
 24. The system according toclaim 3, wherein the CPU outputs a reading hold signal for holdinginstantaneous voltages of the cells in the multicell battery pack and areading balance signal for performing reading and balancing of all cellvoltages.
 25. The system according to claim 10, further comprising avertical interface transmitting the synchronization pulse between themulticell battery packs.
 26. The method according to claim 13, whereinthe synchronization signal comprises a reading hold signal for holdinginstantaneous voltages of the cells in the multicell battery pack and areading balance signal for performing reading and balancing of all cellvoltages.
 27. The method according to claim 14, wherein thesynchronization signal comprises a reading hold signal for holdinginstantaneous voltages of the cells in the multicell battery pack and areading balance signal for performing reading and balancing of all cellvoltages.
 28. The method according to claim 17, further comprising astep of transmitting the synchronization pulse between the multicellbattery packs.